Aphelocoma - Systematics

Systematics

Six species of Aphelocoma are generally recognized currently, since two taxa formerly treated as races of A. coerulescens were recently split off as separate species (A. californica and A. insularis); the 3 now separate species differ in color and bill size. They are believed to have evolved in the Pleistocene, and the Floridan species is known to have been recognizably distinct and present in its current range for at least 2 million years (Emslie, 1996 ). Indeed, the inland and coastal populations of A. californica seem to constitute 2 distinct species too, as might different populations of the Mexican Jay.

• Unicolored Jay, Aphelocoma unicolor – cloudforests of southern Mexico east to Honduras
• Mexican Jay or Gray-breasted Jay, Aphelocoma wollweberi – Sierra Madre Oriental and Sierra Madre Occidental mountains of Mexico, north to southeast Arizona, southwest New Mexico and westernmost Texas, US.
• Transvolcanic Jay, Aphelocoma ultramarina
• Island Scrub Jay, Aphelocoma insularis – Santa Cruz Island off southern California
• Western Scrub Jay, Aphelocoma californica
  • California Scrub Jay, Aphelocoma californica – coastal western North America from Washington to Baja California
  • Woodhouse's Scrub Jay, Aphelocoma woodhouseii - inland western North America, from Oregon through Texas and south to northern interior Mexico
  • Sumichrast's Scrub Jay, Aphelocoma sumichrasti - inland Mexico from Guerrero and Tlaxcala to Oaxaca
• Florida Scrub-Jay, Aphelocoma coerulescens – Florida

mtDNA NADH dehydrogenase subunit 2 sequence data (Rice et al. 2003 ) is unable to properly resolve the relationships of the species. Judging from New World jay biogeography, the Unicolored or Mexican Jays might represent the most basal lineage; morphology would tentatively lean towards the latter which retains more of the group's color patterns, while the available molecular data allows no robust conclusions whatsoever. In any case, the data of Rice et al. (2003) suggests - albeit also with very low confidence - that the Mexican Jay comprises 2 clades which might constitute different species. However, far too few individuals have been sampled to say anything definite on that matter, except that the lineages - if they indeed exist - do not correspond to the geographical pattern of intraspecific variation (see species article for more).

On the other hand, it is somewhat more likely that the Western Scrub Jay is made up of 2 species. These would be separated by the Great Basin, with the Pacific coastal lineage ("California" Scrub Jay) and the Island Scrub Jay, as well as the inland lineage ("Woodhouse's" Scrub Jay) and the Florida Scrub Jay being sister species. This treatment fails to address the problem of birds from inland southern Mexico. What is known about the paleogeography of North America supports these findings, but they must be considered preliminary pending analysis of much more data (Rice et al. 2003 ). Nonetheless, it is actually because the molecular diversity pattern is so badly resolved that it supports the view that rapid Late Pliocene radiation of the North American scrub jays led to the present diversity. Recent studies on the evolutionary history of Aphelocoma jays suggests that all New World jays originated in North America or Mesoamerica (Bonaccorso and Peterson, 2007 ).